Digital Video Broadcast (DVB) is a technique providing multimedia services to a terminal through a digital broadcast network and may be divided into three types according to their transmission modes, i.e., DVB-Terrestrial (DVB-T), DVB-Satellite (DVB-S) and DVB-Cable (DVB-C). Technical specifications for the DVB-S, DVB-C and DVB-T pave the way for high-speed data transmission through satellite, cable and terrestrial video channels respectively. DVB-Handheld (DVB-H) is a transmission standard proposed by the DVB organization for providing multimedia services to a portable/handheld terminal through a terrestrial digital broadcast network. The DVB-H is based on the current DVB-T transmission system and enables a portable/handheld terminal, such as a mobile phone, to receive video broadcast signals steadily by adding additional functions and improved techniques. Compared with a DVB-T terminal, the DVB-H portable/handheld terminal is of lower power-consumption and better performance of mobility and anti-interference. The DVB-H is applicable for portable/handheld terminals, such as a mobile phone and a portable computer to receive signals through the terrestrial digital video broadcast network.
Refer to FIG. 1, which is a schematic diagram of a pilot insertion pattern according to the DVB-T/H. As shown in FIG. 1, each frame consists of 68 Orthogonal Frequency Division Multiplexing (OFDM) symbols. Circles in FIG. 1 denote sub-carriers. And specifically, circles filled with biases denote continual pilots, solid circles denote scattered pilots and hollow circles denote data sub-carriers. Powers of constellations corresponding to the continual pilots and scattered pilots are normalized to 16/9.
Table 1 shows carrier indices for continual pilot carriers in one OFDM symbol according to the DVB-T/H. There are 45 continual pilot carriers for the 2048 Fast Fourier Transform (FFT) mode, i.e., 2K mode, and 89 continual pilot carriers for the 4K mode. Distances separating two continual pilot carriers are not uniform, and the minimum distance separating two continual pilot carriers is three sub-carriers.
TABLE 12K Mode4K Mode0, 48, 54, 87,0, 48, 54, 87, 141, 156, 192, 201, 255, 279, 282, 333,141, 156, 192,432, 450, 483, 525, 531, 618, 636, 714, 759, 765, 780,201, 255, 279,804, 873, 888, 918, 939, 942, 969, 984, 1050, 1101,282, 333, 432,1107, 1110, 1137, 1140, 1146, 1206, 1269, 1323, 1377,450, 483, 525,1491, 1683, 1704, 1752, 1758, 1791, 1845, 1860, 1896,531, 618, 636,1905, 1959, 1983, 1986, 2037, 2136, 2154, 2187, 2229,714, 759, 765,2235, 2322, 2340, 2418, 2463, 2469, 2484, 2508, 2577,780, 804, 873,2592, 2622, 2643, 2646, 2673, 2688, 2754, 2805, 2811,888, 918, 939,2814, 2841, 2844, 2850, 2910, 2973, 3027, 3081, 3195,942, 969, 984,3387, 34081050, 1101,1107, 1110,1137, 1140,1146, 1206,1269, 1323,1377, 1491,1683, 1704
In accordance with the DVB-T/H, when a receiver of a terminal starts up or switches programs, a transmission mode and a length of Cycle Prefix (CP) are determined first, and then after symbol synchronization and correction of fractional frequency offset by the CP, correction of integral frequency offset is implemented by the continual pilots, and then, frame synchronization by Transmission Parameter Signalling (TPS) and channel estimation by the scattered pilots.
There are mainly two methods of frame synchronization by the TPS and further channel estimation by the scattered pilots. Method I: to receive the TPS by non-coherent demodulation, and implement the frame synchronization to determine the locations of the scattered pilots to perform the channel estimation. Method II; to match received signals using a pilot insertion pattern to find the locations of the scattered pilots to perform the channel estimation, receive the TPS by coherent demodulation according to the result of the channel estimation, and then accomplish the frame synchronization. The process of the frame synchronization by the TPS includes: reading 68 OFDM symbols first, demodulating the TPS. If the verification succeeds, it indicates that the 68 OFDM symbols belong to the same frame; otherwise, reading one more OFDM symbol, and demodulate the TPS for the new 68 OFDM symbols. The frame synchronization will not be accomplished until the verification succeeds.
The above methods of frame synchronization by the TPS involves large amount of calculation and the implementations are complex. Moreover, since a frame in the DVB-T/H consists of 68 OFDM symbols, the frame synchronization needs a long period of time and may exceed the duration of a frame, even reach 135 OFDM symbols. In addition, powers of pilot constellations are normalized to 16/9, which only have a power gain of about 2.5 db over those of data constellations. The unobviousness of the power gain of the pilot constellations to the data constellations makes it unfavourable for the frame synchronization, channel estimation and the estimation of the integral frequency offset. Furthermore, the distances separating the continual pilots are not average and the minimum distance separating two continual pilots is only 3 sub-carriers. In the case of the 4K mode, the bandwidth is 8 MHz, the frequency of the centre carrier is 700 MHz. When the frequency offset is −20 ppm˜20 ppm, i.e., when the integral frequency offset is −7˜7 sub-carriers, the distance is unfavourable for the estimation of the integral frequency offset.